Otter board



D. J. GROEN Nov. 28; 1944.

OTTERBOARD Filed June 8, 1942 3 Sheets-Sheet l f..].1 UNITED 1 STATESPATENT Patented Nov. 28, 1944 OFFICE orTEnBoAnD r Donald Julius Groen,Surbiton, England Application June 8, 1942, 'SerialNo.446,320

In Great Britain July 1, 1941 I 4Claims. (01.114435) This inventionrelates to improvements in otterboards and is particularly concernedwith I such devices for use in marine mine sweeping.

operations. An otterboard is used in side sweeping to extend a cableoutwardly from the side of a ship and means are provided such as a floatto prevent the cable from sinking. The tendency for the otterboard tomove away from the side is due to the angle at which it is set to'thedirection of travel but this angle of incidence creates a drag whichretards forward movement and if 1 this angle is decreased to reduce'thedragthe force urging the board away from the ship is also reduced. Itmay be mentioned that on the magnitude of that force depends the lengthof cable which may be used as well as the position at which the boardwill ride with respect to the ship towing it, and hence the area whichmay be swept. I

Now, an object of the present invention is to provide a more eflicientotterboard which rides at a desirably small angle of incidence so thatthere is reduced drag and yetgives an increased forcetending to move itaway from the ship, so

used therewith, or the board will ride at a more favourable position. I

According to the present invention, the otterboard, which is preferablyof streamline, aerofoil, curved or similar form in section seen in plan,has an overall height which is greater than its length. I I To cause theboard to ride at the desired small angle of incidence, the towing cablemay be branched into, or attached to, three, four or more cables orchains which are secured to the board 1 on one side thereof, eitherdirectly or through members projecting from the board, at points.

near the edges thereof, for example, at three points triangularlyarranged, in the four corners of a rectangular board, or otherwise asmay be 1 convenient.

- Further to ensure that the otterboard will ride upright as desired,the lower end thereof may be weighted. I

The oneend of the otterboard maybe longer than the other providingalways that the height be greater and. preferably substantially greaterthan the length but it is further preferred that creased towards the topand bottom either by curving r inclining either the leading or thetrailingedge or by a combination of these possibilities.

Figure 3 is a plan view looking down on Figure 1. i a l I Figures 4, 5and 6 are views similar to Figures 1 to 3 of the same form of otterboardbut having different means for the attachment of ,the towthat eitherlonger or more robust cables may be 2.

ing cable. 7 v

Figure 7 is a side elevation of a modified form of otterboard, and

FigureB isa plan view of the otterboard of Figure7. v Referring now tothe said drawings throughout which like parts bear like reference:numerals and with particular reference to Figures l to 3, the otterboardI, seen in elevation, has the shape of an elongated rectangularparallelogram,

whilst in section as may be seen from Figure 3 it is of aerofoil orstreamline shape. The exact construction of the board is not material tothe present invention as it may be made of wood, or wood and metal, orentirely of metal. The trailing or narrow edge is convenientlyreinforced or protected by a metal or rerlay or reinforcement 2 whichextends down onboth sides. This edge is" also protected by the provisionof two or more projections 3 which serve as feet when the board theboard be symmetrically shaped on opposite sides of a line bisecting itsmajor axis. In the latter casethe length of the board may be deis not inuse and is standing ona ship's deck or other surface. The lower,portion. of the board is desirably similarly protected by a me tallicoverlay or reinforcement 4 which may also be arranged to give additionalweight to that end of the board. The reinforcement 4 may be arranged tocarry an additional weightingportion 5 arranged forwardly of the majoraxis so that most weight is in the region of the forward lower corner ofthe board. e

On the one side of the board which is the substantially fiat side in theform of board, illustrated, there is provided near each corner of theboard a projecting element 6 which is conveniently given a streamlineform as may be seen in Figure 1 which element has an aperture near itsouter end within which is arranged a ring 1 to which may be connected alength of chain or cable 8 in any convenient manner, for example, bymeans of a holding device 9. The four chains or cables 8 are allconnected to a ring In to which the towing cable (not shown) may beattached either directly or through the medium of a short length ofchain ll conveniently by means of a clamping device [2. The lengths ofthe chains or cables 8 may all be substan- \tially the same althoughdesirably the two chains or cables. nearer the forward rounded edge areslightlyshorter than the two chains or cables curves along the portion23 t0 the apex and is similarly curved along the portion 24 to the base.The rear edge 25 is parallel to the corresponding portion of the frontedge 22 and continues as curved portions 26, 21 which match thecurvature of the corresponding portions 23, 24 of the front edge but inopposite sense. The forward rounded portion of the board is protected bya metal reinforcement 28 whilst the rearward portion is similarlyprotected by a metal reinforcement 29. The lower part of theboard isweighted by a weight 3|] which is shaped to conform to v theconfiguration of the board and an extra tom edges. In this way, theotterboard will always tend to ride with its rounded edge foremost in anupright position when, as may be clearly seen from Figure 1 of thedrawings,-its height preferably exceeds its length. The ratio of theheight to the length may vary over wide limits but desirably the ratiois of the order of 2.3:1-to 5:1.

In Figures 4, 5 and 6, is illustrated an otterboard identical with thatillustrated in Figures 1 1 to 3 but having different means forconnectthrough the limbs of a bifurcated connecting ele-' ment i! towhich the towingcable (not shown) may be attached. In this case alsothelengths weight3| is provided i a forward position at on the planeside of the board and the branched ends of the towing cable may beattach-ed directly to the rings 32 or indirectly attached responding tothe cables or chains 8 androds of the rods ti l are substantially thesame, al- I though the. front pair are preferably shorter apart fromdetail variations in length so that the eyes in the ends thereof willstack to be engaged by the bolt I6 as may be seen in Figure-5 and toposition the connecting element l1 nearer to the front edge than therear edge at a point 1 substantially equidistantly spaced from top andbottom edges. When not in use, the connecting element I! may be removed.when the rods, I4 may be collapsed to lie against the board.

Whilst in both of the foregoing examples the towing cable is indirectlyconnected to the board, in the one case through chains or cables 8 andprojecting element 6 and in the. other case through rods M, the towingcable itself may be branched and directly. attached to the board or torings'attached thereto. The points of connection are convenientlysituated as far as possible from one another but the invention is notlimited to. four connection points since there may be three points ofconnection triangularly arranged as is later described with referenceto" a modified form of otterboard shown in Fig ures '7 and 8, or theremay be more than four connection points say five in number, v as may bemost convenient having regard to the size of the board or the particularconnection employed.

' The otterboard shown in Figures 7 and 8 may be of similar generalconstruction to the otterboards already described butisdifferentiatedin- [4 already described, the arrangement in any casedesirably being such that the point of divergence of the branched endsof the towing cable or of the auxiliary attachment means-is situatedforwardly along a line which bisects the major axis of the board. As inthe previous example, the reinforcement 29 is provided with feet 3.

It will be appreciated from the foregoing examples that the boardisdesirably of symmetrical shape on opposite sides but its shapes are notlimited to the examples above given since the forward edge may inclineaway from the mid point or be curved away from that point whilst therear edge may be straight throughout its length or vice versa andalthough, such anarrangement is preferred it is not essential since insome cases the length of the board may be determined by the respectivelengths of the cable branches or the indirect attachment means and thearrangement is such that the board is arranged to ride, at a minimumpractical angle of,

incidence; I v i ,7

By causing the otterboard to ride at a lesser angle of incidence than isnow customary, the drag set up by the device is reduced, but this doesnot reduce the forcetending to move the device away from the ship since,due to the fact that its height exceeds its length and its preferredhorizontal sectional shape that .force is increased or in other wordsthe board has. a greaterlift. As th drag is reduced andthe said forceisin: creased, the otterboard may ride at a more favourable position inrelation to the ship towing it, a longer towingcable maybeused' so. thatduring mine sweeping operations a wider-field. may be swept, a morerobust cable may be used, 'the towing operation carried outwitha lesserexpenditureof energy, or a combinationaof these possibilities to achievegreater'efiiciencyi- 1. An otterboard'of aerofoil section which has anoverall height whichis greater than itslength; at least three projecting'elementsof streameline form on one side ofsaid board, to the ends ofwhich. elements are connectedthe endsofzele ments connected to a towingcable, means for weighting the lower portion of the board and additionalweighting means for weighting the lower forward portion of the board.

2. An otterboard of aerofoil section which has an overall height whichis greater than its length,

at leastthree projecting elements of streamline form on one side of saidboard, chains connected to the ends of said elements, means forconnecting the free ends of-said chains and for connecting them to atowing cable, and means for weighting the lower portion of the board.

3. An otterboard of aerofoil section which has an overall height whichis greater than its average length which is of diminishing extent inboth directions away from the middle of the board,

connecting means leading from at least three points on the one side ofsaid board, a towing connector common to all said connecting means,

to which elements are attached to receive the connection of a towingcable, anda plurality of weighting means at the lower portion of theboard, with, one of said weighting means wholly forward of the majoraxis of the board.

DONALD JULIUS GROEN,

